1. Field of the Invention
The present invention relates to a method for manufacturing a modular board to be electrically connected to a mother board via soldering.
2. Description of the Related Art
In order to achieve high-density design, current electrical circuits are partially assembled into a modular board to facilitate intermediate inspection and mounting, and the modular board is then mounted on a mother board (as disclosed in Japanese Unexamined Patent Application Publication No. 63-204693).
Such conventional modular boards include a rectangular and thin insulator board which is fabricated by alternately laminating insulation resin materials and conductive wiring patterns.
Mounted on the modular board are active elements such as transistors, and passive elements such as resistors and capacitors. These elements are interconnected by a wiring pattern and define an electrical circuit. The end surface portion of the edge of the modular board has a plurality of end surface through holes which are filled with edge electrodes for feeding power from a mother board external to the electrical circuit and inputting and outputting signals to and from the electrical circuit.
The modular board thus includes a modularized electrical circuit assembled thereon for performing a desired signal process on signals input from the mother board. During assembly, the modular board is stacked on the mother board, and the edge electrodes are connected to electrical pads on the mother board using soldering to mount the modular board on the mother board.
The above-referenced modular board is fabricated by alternately laminating rectangular insulators of resin material and conductive wiring patterns.
Since a thermal expansion ratio is different between the resin material of the board and the wiring, the board partially suffers from distortion such as warpage depending on the layout and density of the wiring pattern when the board is heated during the process of the board or during the soldering of the board.
In the conventional art, the modular board is often partially separated from the mother board due to warpage when the modular board is mounted on the mother board. The warpage of the modular board leads to a connection failure on some of the edge electrodes, thereby deteriorating the reliability of the modular board. The conventional modular board is configured to be as thin as possible, and is thus subject to increased warping even under a slight degree of heating. Therefore, it is difficult to reliably mount the modular board onto the mother board.
To overcome the above-described problems with the prior art, preferred embodiments of the present invention provide a method of manufacturing a modular board which enables edge electrodes to be securely connected to a mother board even when the modular board is subject to warpage.
One preferred embodiment of the present invention provides a method for manufacturing a modular board and includes the steps of opening a through-hole in a bare board, providing a back electrode surrounding the through-hole on the bottom surface of the bare board, arranging an edge electrode, connected to the back electrode, partially or entirely on the inner wall of the through-hole, cutting the bare board along the through-hole to produce a split board having the back electrode and the edge electrode and a remaining bare board, providing an adhesive compound containing an oxide removal substance on the periphery of the through-hole, attaching solid solder to the adhesive compound, heating the split board and the remaining bare board to melt the solid solder, and cooling and solidifying the molten solder on the edge electrode and the back electrode for bonding.
The split board having the back electrode and the edge electrode and the remaining bare board are preferably formed from the bare board. By placing the split board back into the remaining bare board, the through-hole is again provided between the split board and the remaining bare board. In this way, the split board is separated from the bare board prior to attaching the solid solder to the edge electrode.
The solid solder is held in position by the adhesive compound because the adhesive compound containing the oxide removal substance is provided around the through-hole followed by the placement of the solid solder on the adhesive compound. When the split board and the remaining bare board are heated, the adhesive compound acts as a catalyst, and the solid solder starts melting at the portion thereof in contact with the adhesive compound and flows into the through-hole. Since the edge electrode is provided in the through-hole, the molten solder securely attaches to the edge electrode. A portion of the molten solder flows from the edge electrode and covers the back electrode.
Since the molten solder has a substantially spherical shape and surface tension and attaches to the edge electrode and the back electrode, a portion of the molten solder swells and expands out of the through-hole. When the split board, which has already been cut from the bare board, is separated from the bare board, the split board becomes a modular board, and the molten solder swells from the bottom surface thereof toward the mother board. The swollen solder is drawn into a gap between the modular board and the mother board, thereby securely connecting the edge electrodes of the modular board to the electrical pads of the mother board.
Another preferred embodiment of the present invention provides a method for manufacturing a modular board and includes the steps of providing a back electrode on the bottom surface of a bare board, opening a through-hole in the bare board in the back electrode, arranging an edge electrode, connected to the back electrode, partially or entirely on the inner wall of the through-hole, cutting the bare board along the through-hole to produce a split board having the back electrode and the edge electrode and a remaining bare board, providing an adhesive compound containing an oxide removal substance on the periphery of the through-hole, attaching solid solder to the adhesive compound, heating the split board and the remaining bare board to melt the solid solder, and cooling and solidifying the molten solder on the edge electrode and the back electrode for bonding.
The method for manufacturing a modular board preferably includes the step of removing the back electrode on the bottom surface of a portion of the bare board becoming the remaining bare board and the edge electrode on the inner wall of the through-hole of the portion of the bare board becoming the remaining bare board, prior to the cutting of the bare board.
This arrangement prevents the molten solder from sticking to the remaining bare board. After the molten solder is cooled and solidified, the split board is easily separated from the remaining bare board.
The adhesive compound is preferably provided, on the top surface of the split board, in contact with the edge electrode.
When the split board is heated with the solid solder attached to the adhesive compound, the solid solder begins melting at the portion thereof in contact with the adhesive compound. Since the adhesive compound remains in contact with the edge electrode, the molten solder attaches to the edge electrode while partially flowing along the edge electrode to cover the back electrode. As a result, the solder bonds to both the edge electrode and the back electrode.
The adhesive compound is preferably provided on the bottom surface of the split board and in contact with the back electrode.
When the split board is heated with the solid solder attached to the adhesive compound, the solid solder begins melting at the portion thereof in contact with the adhesive compound. Since the adhesive compound remains in contact with the back electrode, the molten solder attaches to the back electrode while partially flowing along the back electrode to reach the edge electrode. As a result, the solder bonds to both the edge electrode and the back electrode.
The adhesive compound is preferably provided in the vicinity of the through-hole on one of the top surface and the bottom surface of the remaining bare board.
When the split board is heated with the solid solder attached to the adhesive compound, the solid solder starts melting at the portion thereof in contact with the adhesive compound. Since the adhesive compound remains in the vicinity of the opening of the through-hole, the molten solder spreads over the opening while, at the same time, flowing into the through-hole. The molten solder is in contact with and attaches to the edge electrode within the through-hole while partially flowing along the edge electrode and reaching the back electrode. As a result, the solder bonds to both the edge electrode and the back electrode.
The solid solder is preferably attached onto the adhesive compound with the through-hole blocked.
This arrangement allows the molten solder to flow into the through-hole when the solid solder becomes molten through heating. The solder thus reliably bonds to the edge terminal within the through-hole.
Another preferred embodiment of the present invention provides a method for manufacturing a modular board and includes the steps of opening a through-hole in a bare board, providing a back electrode surrounding the through-hole on the bottom surface of the bare board, arranging an edge electrode, connected to the back electrode, partially or entirely on the inner wall of the through-hole, cutting the bare board along the through-hole to form a split board having the back electrode and the edge electrode and a remaining bare board, attaching solid solder onto the edge electrode, providing an adhesive compound containing an oxide removal substance onto the solid solder prior to or subsequent to the attachment of the solid solder, heating the split board and the remaining bare board to melt the solid solder, and cooling and solidifying the molten solder on the edge electrode and the back electrode for bonding.
When the split board is heated with the solid solder attached onto the edge electrode, the solid solder attaches to the edge electrode while becoming molten. The molten solder partially flows along the edge electrode, thereby covering the back electrode. As a result, the solder bonds to both the edge electrode and the back electrode.
Yet another preferred embodiment of the present invention provides a method for manufacturing a modular board and includes the steps of providing a back electrode on the bottom surface of a bare board, opening a through hole in the bare board in the back electrode, arranging an edge electrode, connected to the back electrode, partially or entirely on the inner wall of the through-hole, cutting the bare board along the through-hole to produce a split board having the back electrode and the edge electrode and a remaining bare board, attaching solid solder to the edge electrode, providing an adhesive compound containing an oxide removal substance on the solid solder prior to or subsequent to the attachment of the solid solder, heating the split board and the remaining bare board to melt the solid solder, and cooling and solidifying the molten solder on the edge electrode and the back electrode for bonding.
Preferably, the method for manufacturing a modular board further includes the step of removing the back electrode on the bottom surface of a portion of the bare board becoming the remaining bare board and the edge electrode on the inner wall of the through-hole of the portion of the bare board becoming the remaining bare board, prior to cutting the bare board.
This arrangement prevents the molten solder from sticking to the remaining bare board. After the molten solder is cooled and solidified, the split board is easily separated from the remaining bare board.
Preferably, the solid solder blocks the through-hole or is accommodated in the through-hole.
The solid solder is thus securely held in position by the through-hole. When the solid solder is melted, the molten solder easily attaches to the edge electrode arranged in the inner wall of the through-hole.
A further preferred embodiment of the present invention provides a method for manufacturing a modular board and includes the steps of opening a through-hole in a bare board, providing a back electrode surrounding the through-hole on the bottom surface of the bare board, arranging an edge electrode, connected to the back electrode, on the inner wall of the through-hole, partially removing the inner wall of the through-hole to form a slit to form a pre-split board including the edge electrode and the back electrode, the pre-split board being surrounded by the slit, providing an adhesive compound containing an oxide removal substance on the periphery of the edge electrode, attaching solid solder to the adhesive compound, heating the pre-split board and the remaining bare board to melt the solid solder, cooling and solidifying the molten solder on the edge electrode and the back electrode for bonding, and thereafter separating the pre-split board as the modular board from the bare board at the position of the slit.
The pre-split board having the edge electrode and the back electrode is produced by forming the slit in the bare board. The solid solder is held in position by the adhesive compound because the adhesive compound containing the oxide removal substance is provided around the edge electrode followed by the placement of the solid solder on the adhesive compound. When the split board and the remaining bare board are heated, the adhesive compound acts as a catalyst, and the solid solder starts melting at the portion thereof in contact with the adhesive compound and flows into the through-hole. Since the edge electrode is mounted in the through-hole, the molten solder attaches to the edge electrode. A portion of the molten solder flows from the edge electrode to cover the back electrode. Since the molten solder has a substantially spherical shape with surface tension and attaches to the edge electrode and the back electrode, a portion of the molten solder swells out of the through-hole.
Another preferred embodiment of the present invention provides a method for manufacturing a modular board and includes the steps of providing a back electrode on the bottom surface of a bare board, opening a through-hole in the bare board in the back electrode, arranging an edge electrode, connected to the back electrode, on the inner wall of the through-hole, partially removing the inner wall of the through-hole to form a slit to produce a pre-split board including the edge electrode and the back electrode, the pre-split board being surrounded by the slit, providing an adhesive compound containing an oxide removal substance on the periphery of the edge electrode, attaching solid solder to the adhesive compound, heating the pre-split board and the remaining bare board to melt the solid solder, cooling and solidifying the molten solder on the edge electrode and the back electrode for bonding, and thereafter separating the pre-split board as the modular board from the bare board at the position of the slit.
The adhesive compound is preferably provided, on the top surface of the pre-split board, in contact with the edge electrode.
When the split board is heated with the solid solder attached to the adhesive compound, the solid solder begins melting at the portion thereof in contact with the adhesive compound. Since the adhesive compound then remains in contact with the back electrode, the molten solder attaches to the back electrode while partially flowing along the back electrode to cover the edge electrode. As a result, the solder solidifies and bonds to both the edge electrode and the back electrode.
The adhesive compound is preferably provided, on the bottom surface of the pre-split board, in contact with the back electrode.
When the split board is heated with the solid solder attached to the adhesive compound, the solid solder begins melting at the portion thereof in contact with the adhesive compound. Since the adhesive compound remains in contact with the back electrode, the molten solder attaches to the back electrode while partially flowing along the back electrode to cover the edge electrode. As a result, the solder solidifies and bonds to both the edge electrode and the back electrode.
The solid solder is preferably attached to the adhesive compound at a location corresponding to the edge electrode with the slit partially blocked.
When the solid solder is melted via heating, the molten solder enters into the slit at the location corresponding to the edge electrode. The solder reliably attaches to the edge electrode exposed within the slit.
Still another preferred embodiment of the present invention provides a method for manufacturing a modular board and includes the steps of opening a through-hole in a bare board, providing a back electrode surrounding the through-hole on the bottom surface of the bare board, arranging an edge electrode, connected to the back electrode, on the inner wall of the through-hole, partially removing the inner wall of the through-hole to cause a slit to form a pre-split board including the edge electrode and the back electrode, the pre-split board being surrounded by the slit, attaching solid solder to the edge electrode, providing an adhesive compound containing an oxide removal substance onto the solid solder prior to or subsequent to the attachment of the solid solder, heating the pre-split board and the remaining bare board to melt the solid solder, cooling and solidifying the molten solder on the electrode and the back electrode, and thereafter separating the pre-split board as the modular board from the bare board at the position of the slit.
When the pre-split board is heated with the solid solder attached to the adhesive compound, the solder attaches to the edge electrode while being melted. The molten solder flows along the edge electrode and covers the back electrode. As a result, the solder solidifies and bonds to both the edge electrode and the back electrode.
Yet another preferred embodiment of the present invention provides a method for manufacturing a modular board and includes the steps of providing a back electrode on the bottom surface of a bare board, opening a through-hole in the bare board in the back electrode, arranging an edge electrode, connected to the back electrode, on the inner wall of the through-hole, partially removing the inner wall of the through-hole to make a slit to form a pre-split board including the edge electrode and the back electrode, the pre-split board being surrounded by the slit, attaching solid solder onto the edge electrode, providing an adhesive compound containing an oxide removal substance onto the solid solder prior to or subsequent to the attachment of the solid solder, heating the pre-split board and the remaining bare board to melt the solid solder, cooling and solidifying the molten solder on the edge electrode and the back electrode, and thereafter separating the pre-split board as the modular board from the bare board at the position of the slit.
Preferably, the solid solder partially blocks the slit at a location corresponding to the edge electrode, or is accommodated within the slit at a location corresponding to the edge electrode.
The solid solder is thus securely held in position by the slit. When the solid solder melts, the molten solder easily attaches to the edge electrode arranged in the inner wall of the slit.
Another preferred embodiment of the present invention provides a method for manufacturing a modular board and includes the steps of opening a through-hole in a bare board, providing a back electrode surrounding the through-hole on the bottom surface of the bare board, arranging an edge electrode, connected to the back electrode, partially or entirely on the inner wall of the through-hole, providing an adhesive compound containing an oxide removal substance on the periphery of the through-hole, attaching solid solder to the adhesive compound, heating the bare board to melt the solid solder, cooling and solidifying the molten solder on the edge electrode and the back electrode, and thereafter cutting the bare board at the position of the through-hole to separate the modular board.
When the bare board is heated with the solid solder attached to the adhesive compound, the adhesive compound acts as a catalyst, and the solid solder begins melting at the portion thereof in contact with the adhesive compound and flows into the through-hole. Since the edge electrode is mounted in the through-hole, the molten solder attaches to the edge electrode. A portion of the molten solder flows from the edge electrode and covers the back electrode.
Since the molten solder has a substantially spherical shape with surface tension and attaches to the back electrode, a portion of the molten solder swells out of the through-hole. When the modular board is formed by cutting the bare board, the swollen solder fills a gap between the modular board and the mother board, thereby connecting the edge electrodes of the modular board to the electrical pads of the mother board.
Another preferred embodiment of the present invention provides a method for manufacturing a modular board and includes the steps of providing a back electrode on the bottom surface of a bare board, opening a through-hole in the bare board in the back electrode, arranging an edge electrode, connected to the back electrode, partially or entirely on the inner wall of the through-hole, providing an adhesive compound containing an oxide removal substance on the periphery of the through-hole, attaching solid solder to the adhesive compound, heating the bare board to melt the solid solder, cooling and solidifying the molten solder on the edge electrode and the back electrode, and thereafter cutting the bare board at the position of the through-hole to separate the modular board.
Preferably, the method for manufacturing a modular board according to this preferred embodiment further includes the step of removing the back electrode on the bottom surface of a portion of the bare board becoming the remaining bare board and the edge electrode on the inner wall of the through-hole of the portion of the bare board becoming the remaining bare board, prior to the providing of the adhesive compound.
This arrangement prevents the molten solder from sticking to the remaining bare board other than the modular board subsequent to the cutting. When the molten solder is cooled and solidified, the split board is easily separated from the remaining bare board without the need for cutting the solder bonded to the edge electrode.
Preferably, the adhesive compound is one of a flux and a solder paste including a powdered solder and a flux, and the solid solder is a spherical solder ball which is solidified from a brazing alloy.
With the flux or the solder paste, the solder ball is held in position and solder melting is expedited. When the flux is used, the volume of the molten solder ball is maintained, and the dimension of the bump from the bottom surface of the board is constant. When the solder paste is used, the solder ball is melted together with the solder paste. The molten solder ball together with solder in the solder paste solidifies and bonds to both the edge electrode and the back electrode.
Other features, elements, characteristics and advantages of the present invention will become apparent from the detailed description of preferred embodiments thereof with reference to the attached drawings.